1. Field of the Invention
The present invention relates to a display device, and more particularly to a display device which includes a common electrode drive circuit adopting an every-line-independent common AC drive method.
2. Description of the Related Art
A liquid crystal display module adopting a TFT (Thin Film Transistor) system has been popularly used as a display device of a portable equipment such as a notebook-type personal computer. Particularly, a liquid crystal display module which includes a miniaturized liquid crystal display panel is used as a display device of a portable equipment such as a mobile phone which a user always carries with him/her, for example.
In general, when the same voltage (DC voltage) is applied to a liquid crystal layer for a long time, the tilting of the liquid crystal layer is fixed and, eventually, an image retention phenomenon is induced thus shortening a lifetime of the liquid crystal layer.
To prevent such a drawback, in the liquid crystal display module, the voltage applied to the liquid crystal layer is alternated for every fixed time. That is, using a voltage applied to a common electrode as the reference, the voltage applied to pixel electrodes is changed to a positive voltage side and a negative voltage side for every fixed time.
As a drive method for applying the AC voltage to the liquid crystal layer, there has been known a common inversion method which inverts a voltage applied to a common electrode to two potentials, that is, the potential at a high potential side and a potential at a low potential side. As one such common inversion method, a drive method which independently alternates a voltage applied to the common electrode for every line (also referred to as an every-line independent common AC drive method) is described in JP-A-2001-194685 (patent document 1) which is a document related to the present invention.
The every-line independent common AC drive method described in the above-mentioned patent document 1 uses an IPS (In Plane Switching) liquid crystal display panel, wherein the voltage applied to the common electrodes on respective display lines is independently alternated for respective lines. According to the drive method of the present invention, it is possible to decrease a voltage width of a gate voltage supplied to scanning lines.